Fluted lamp lens



April 26 1927' c. E. GODLEY FLUTED LAMP LENS Filed May 1926 2 Sheets-Sheet 1 Patented Apr. 26, 1927.

OHARLES E. GODLEY, OF DETROIT, MICHIGAN, ASSIGNOR,'BY MESN'E ASSIGNMENTS,

1'0 C. M. HALL LAMP COMPANY, A CORPORATION OF MICHIGAN.

FLUTED LAMP LENS.

Application filed ma a,

My invention relates to fluted or grooved translucent light-transmitting elements. such as headlight lenses. Where light projected through aglass pane or lens is to spread 5 along one general plane, it has long been customary to accomplish this spreading by making the rear face of the glass and providing the forward face with prisms or grooves extending transversely of the direction in which the light is to be spread.

In automobile headlights, forwardly convex formations on the lens are objectionable because the light is so refracted by the junctures of the consecutive prisms that dark streaks are left on the road. While these 4 dark streaks can be avoided by providing the forward face of the lens with grooves having arcs of circles as their transverse sections, such grooved lenses have three objections,

with light projected through the lens byan accurately formed parabolic reflector which.

has the source of light at its focus.

One of these objections lies in the irregular distribution of the projected light, which makes it necessary to select an approximately suitable groove radius by a long series of tests of difl'erent sections 'and which leaves aconsiderable portion of the light spread beyond the diiersive angleneeded in an automobile head I power of the lamp bulbs which are allowed to be used in such headlights, this waste of light should be avoided.-

Another objection, .in practice, lies in the fact that vertical grooves of circular sections concentrate part .of the light unduly ateither s ide' of the beam, thereby producing a pair of laterally spaced bright spots on the road. A third objection hes in he fact that such circular I too large a percent groove sections spread ageof the light at considerable anglesfrom the vertical medial plane of the pro ected beam, thereby I proportion of the light in the direct-path of 'the vehicle. j

.. -M v present invention aims to overcome particularly when used in connection ght. Owing to the low candlewhich is more serious.-

leaving an undesirably small zontal section all of these objections by providing" lens 19%. serial No. 107,096

groove sections which have five "distinct adto be" easily and accurately predetermined for any desired angular spread.-

(4) Avoiding both bright and dark spots or streaks on the road.

(5) Afl'ording a projection of light on the v road which gradually decreases from amaximum in the'medial vertical plane of thebeam to a minimum at the lateral edges of the beam.

Furthermore, my ll'lVBIltlOIl. provides lens grooves for this purpose which will minimize the efiect offrain on them. Illustrative of my invention, Fig. 1 is a front view of a headlight lens grooved ac- ,cording to itand designed for refracting a light which is projected through the lens from the back' of the lens in rays-perpendicularto the flat rear face of the-lens, so as to distribute the light within a definitely limited angle and with an intensitygradually decreasing in both directions laterally of the axis of the lens. 3

Fig. 2 is a fragmentary and-emerged section taken throughthe lens at right anglesto the direction in which the grooves extend. Fig, 3 is a diagram showing the method of'determiningthe shape of the groove for agiven-maximum spread of light.

Fig. 4 isan enlargement of a portion of .Fig; 2, with the lens reduced in thickness and with lines showing the refraction of the rays of light passing through spaced points, namely points spaced equally distant along the rear flat face of the lens along a line at right angles to the axis of the groove, and.

also showing the projection ofrays along these lines against a screen parallel to the lens. i

- Fig. 5 is a fragmentary and enlarged horithrough a lens in which each groove-comprises a'djoined portions-of dif ferent ellipse, so as to distribute the light within different angles at opposite sides of the medial vertical plane through the lens.

In accomplishing the purposes of my invention in the lens of an automobile headlight, I provide the front face of the lens with vertical grooves, each groove having a section which is a portion of an oval having its major axis substantially parallel-to the flat rear face of the lens. act predetermining of the angles within which the light is distributed at each side of the medial vertical plane of the beam, I preferably make one or more curve portions for this groovesection, each portion being part of an ellipse which has its major axis parallel to the flat face of the lens.

Where the light is to be distributed symmetrically at both sides of the vertical medial plane of the projected beam, I make-the entire groove section a part of a single ellipse and preferably employithe part of one side of the ellipse which is between the two loci lines at right angles through the major axis of the ellipse and extending respectively through the two foci of the ellipse, thereby facilitating the determining of the elliptical curvature for a given angle of light distribution.

Illustrative of the procedure in such a case, the diagram of Fig. 3 shows the staight line A as denoting a horizontal section through the fiat rear face of the lens,

7 with locus lines B and 0 extending at right angles'to the line A and spaced b the desired width of the groove, while t e points I) and E are respectively spaced along the locus lines B and C at equal distances from the line a.

To determine a groove sectionwhich will give a maximum spread at opposite sides of the lines B and C corresponding to a desired limiting angle F, I' draw a 'line G through the oint D at the forwardly directed. acute 'imitinlg an le F. I then draw another line H t rough the point D at such an an le I to the line B, and at the opposite si e of the latter from the line- (Jr'that the proportion between the angle I and the angle K (or the 'acute angle be,- tweenthe lines G and H) will be as 1 to the, refractive index of the glass of which the lens is to be made. Thus, if the refractive index of the glass is 1.56, the angle I would be or approximately 2.78 times the angle F. V The line H as thus located willjbo the disector ofthe angle formed b the straight lines B and L runningth'roug the poi'ntD on the desired elli se to'thetwo foci of th'e ellipse, hence I v drawing .it through D at an aci' te an gleM eter'mine the line L by equal to the angle I 'butatthe opposite side of the line H from the latter angle. The

To permit an ex intersection N of the line L with the otluar locus line C gives me one focus of the ellipse, so that an ellipse drawn with the points N and O as foci and with D as one point on the ellipse will have the'desired curvature. In practice, the form of the elli se can thus be determined on a greatly'en arged scale and afterwards reduced in its proportions to correspond to the desired actual widtn of the groove.

Owing to the above recited definite relationships, I can also readily calculate the maximum spread of light resulting from a groove which has as its curve section B the portion of-agiyen ellipse between the locus lines B and C of that ellipse. To do this,

I simply bisect the angle between one of the glass, gives me the angle It at which light passing along the line B througu the point.

D will be refracted away from the bisector (or normal) line H at this point D, hence this angle is easily fi ured so as to draw the line G at the calcu ated angle from the bisector or normal line H. Then the acute angle between the line G and the locus line B (or initial direction of the ray of light) shows the maximum lateral refraction of light at each side of the initial direction of the rays of light, or one-half the maximum angle of light dispersion.

'W'ith a lens groove having such an ellipse 'portion as its transverse section, Fig. 4 is a plotting of the rays of light passing throu h the lens at right angles to the rear face i of the lens. This shows that rays S spaced at equal distances along this rear face transversely of the groove are refracted at angles which increase gradually according to the increasing initial distance of these rays from the medial lane M of the groove. Since the initial spacings of the consecutive rays S were e ual while the intersections of the refracted ra s with a screen W disposed parallel to t e rear face of the lens increase gradually at opposite sides of the medial plane M, the illumination of the screen" is-most intense along that medial plane and diminishes uniformly in opposite iness and. a definite 'predetermining of the angle of spread.

owever, the groove section! thus employed need not allbe a part of a single "e p 'I'Inay use adjoined curve portions merging. smoothly into each other and each forming part of an ellipse which has lit) its major axis parallel to the flat rear face of the lens. For example, the groove section in Fig. 5 comprises a part T curved for distributing light within the angle F at one side of the axis of the beam. and a continuation part U designed for distributing light within a smaller angle V at the other side of this axis. In determining such a groove, the general shape of each ellipse (or proportion between the major and minor axes) is determined as heretofore recited. and one of these is reduced in. dimensions as before,-

thereby determining the effective groove depth W, after which the other is reduced to give the same groove depth. Then the two reduced elliptical portions are adjoined at a point where they afford smooth continuations of each other.

With such an unsymmetrical groove section, as with the previously'described symmetrical groove section, the intensity of the light is greatest near the medial vertical plane of the beam and decreases toward either side of the beam with such graduated uniformity as to eliminate streaks and spots on the road.

While, the width of such grooves could be varied greatly, I have found a decided difference in the effect of rain on such vertically grooved lenses, according as the grooves are more or less than about a quarter of an inch in width. .VVith the groove more than a quarter of an inch wide, the average rain drop which strikes a single groove is spread laterally to such an extent that the capillary action overcomes gravity and causes the drop to adhere ,to the lens or at best to descend very slowly. On the other hand, if such an average rain drop strikes a groove which is not more than aquarter of an inch in width, this limited groove width will correspondingly restrict the proportion of the surface of the drop which engages the glass, so that the capillary action is insuflicient to overcome the weigh of the drop and the latter travels speedily 7 down the groove. Hence my lens automatically and speedily sheds the rain drops when constructed with this maximum groove width, thereby greatly increasing the penetration of the beam of light and the safety of driving o'n-rainy nights. 7 f

However, while I have illustrated my invcntion as embodied in a lens which has its entire light emitting face formed into vertical grooves. I do not wish to be limited to this embodiment, it being obvious that changes might be made without departing either from the spirit of my invention or from the appended claims. or do I wish to-be limited to the use of such elliptically grooved glass as a portion of a headlight having a parabolic reflector.

T claim as my invention: I

l. A lens for spreading light laterally the said rays respectively reach the opposite edges of the groove, the ellipsebemg of Such a'curvature that the angle between the direction on which the ray reaching each groove section end along one of the said lines and the bisector of the angle between strai ht lines connecting the said end with the oci of the ellipse is equal to one half of the last named angle multiplied by the refractive index of the glassof which the lens is made.

2. For use in the lateral spreading of parallel horizontal rays, a lens having one face in ageneral plane at right angles to the said rays, the said lens face being provided with-vertical grooves each having as its horizontal section that portion of a determining ellipse which is disposed at one side of the major axis of the ellipse and which is between the locus lines extending at right angles to the axis of the ellipse through the foci thereof; the major axis of the determining ellipse bein horizontal and parallel to the said genera plane; the determining ellipse being such that the acute angle between either of the said-loci lines and the direction in which light is refracted from the point of the ellipse on that locus line is approximately fifty-six one-hunat the same point. V

3. A method of designing a transverse groove section for the face-of a glass lens and having light directed to the lens in rays at right angles to the general plane of the said face, when the grooved lens portion is to refract rays within a limiting angle of deviation from the direction of the said rays transversely of the groove; the

said. method consisting of laying out end points spaced to correspond to the width of the groove, drawing locus lines at rightangles to a line connecting the said enddredths of the acute angle between the same locus line and a line normal to the-ellipseof which the lens is to be made; drawing a 13 focus line through the last named point end diverging from the last-namexl locus line at an'angle double that by which the bisector line diverges from the saiol locus line, and drawing an ellipse passing through the said end points aid having its major axis parallel to the straight line connecting the end points, the ellipse having its loci respectively on the locus lines and having one focus at the intersection of the said focus line with'the locus line passing through the In other enol point Signed at Detroit, Michigan, April 28th,

CHARLES 1e. GODLEY. 

